The present invention relates to a recording face identifying device used to detect an initialized direction of magnetization of a magneto-optic record medium such as an a magneto-optic disk to identify the recording face.
Recording and reproducing systems for magneto-optic disks will be briefly explained below. The magneto-optic disk is an optical magnetic record medium having a magnetic film on a disk substrate whose easy-axis of magnetization is in a direction perpendicular to the film surface. Recording, reproducing or erasing of information is performed by projecting a light beam focused to about 1 .mu.m diameter by an objective lens onto the magneto-optic film surface on the disk.
To record information, a biasing magnetic field whose direction is reverse to an initialized direction of film magnetization is applied to the magnetic disk and the light beam which is intensity-modulated in response to a recorded signal is projected onto the film surface. Film portions projected by the intense light beam rise partially in temperature and the coercive forces of the portions are reduced. Therefore, the magnetized directions of the portions are reversed in the direction of the biasing magnetic field. Thus, magnetic recording corresponding to the intensity modulation of the recording signal can be effected.
To reproduce the recorded portions, the light beam is projected on the disk and its reflected beam is detected. The light beam is a linearly polarized laser beam with the polarized direction known. When such a light beam is projected onto the magnetized film, its reflected light beam produces a slant in the plane of polarization corresponding to a magnetized condition caused by a magneto-optic effect (Kerr effect). Therefore, the slant of the plane of polarization of the reflected light beam is detected by an analyzer and its output is transduced into an intensity of light and its intensity is detected by a photodetector. This enables the system to reproduce the recorded signal.
In practice, in order to enhance S/N, this reflected light beam is split into a P polarized light component and a S polarized light component which intersect at right angles. These two light intensities are detected by two photodetectors respectively. By determining a difference between these two outputs from the two photodetectors, the system can reproduce the recorded signal.
As mentioned above, a magneto-optic disk subjected to recording or reproducing of information is formed with magnetic films, normally, on both sides of the disk and information can be separately recorded on both sides of the disk, for example, A face and B face. Magnetizations of the films on A face and B face are initialized in the same direction, therefore, when loading the magneto-optic disk into a magneto-optic disk device, the initialized direction of magnetization viewed from the device side is reversed between A face setting and B face setting.
Therefore, when recording, the initialized direction of magnetization must be recognized and the biasing magnetic field must be applied in the reverse direction with respect to the magnetized direction.
In a conventional magneto-optic disk device, an identification mark for identifying A face and B face is provided on a cartridge case housing of the magneto-optic disk such that when loading the disk, the initialized direction of magnetization is recognized by mechanically detecting or electrically detecting this mark.
However, provision of such an identification mark on the cartridge case of the magneto-optic disk requires a separate detector used only for detecting the identification mark loading to increased costs.
Further, the initialized direction of magnetization has been indirectly detected by using such an identification mark, thereby rendering it difficult to know whether an indication of the identification mark on the cartridge case conforms with the real initialized direction of magnetization on the disk.
When using a magneto-optic disk having only one side magnetic film, the initialized direction of magnetization must be detected by the device unless the direction is standardized. Thus, in this case the mark indicating the initialized direction of magnetization on the cartridge case is also necessary. The same problem as that encountered in using a both sides magnetic film disk is found in a single-sided disk.